Rotary axial piston pumps (RAPPs) are known in the art and can be constructed for a number of different end-use applications. One category of RAPPs are configured for use in applications, e.g., oil hydraulic transport, that permit the internal components that are subjected to friction to be oil lubricated, thereby helping to reduce the unwanted effects of friction to provide a desired service life.
Another category of RAPPs are configured for use in applications, e.g., water hydraulic transport, that do not permit the internal components subjection to friction to be oil lubricated. In such applications, the RAPPs are configured to use plain water without additives or aides as the only friction lubricating medium.
Conventional RAPPs configured for water hydraulic transport service use internal parts, subjected to friction during use, that are specifically configured to include a polymeric low-friction surface feature. Such a conventional RAPPs comprise metallic piston slippers that include a polymeric surface feature that projects outwardly a small distance from the slipper body metal interface surface. As the piston rotates against a metallic swash plate during RAPP operation, and the polymeric surface feature operates to prevent metal-to-metal contact, thereby reducing friction.
While such RAPPs are configured to address frictional wear effects between adjacent metallic parts during water hydraulic transport use, the use of such RAPPs configured in the manner described require that the water entering the pump be filtered to very high level to remove particulate matter. If unfiltered, the particulate matter in the water can otherwise wear and/or damage polymeric surface feature resulting in metal-to-metal contact, thereby reducing the effective service life of the RAPP. The need to filter the water transported by the RAPPs to protect against unwanted damage and/or reduced service life involves using filtration equipment that adds labor and material costs to the overall cost of operating such RAPPs.
Thus, while RAPPs configured for water transport service are constructed to provide some degree of low friction operation under certain operating conditions, e.g., ultra-clean conditions, it is desired that an RAPP be constructed in a manner that permits a more robust operating parameters in water transport services in terms of both improved service life and in terms of reduced water pretreatment requirements. Specifically, it is desired that an RAPP be constructed in a manner comprising internal parts specially developed and engineered to provide an improved degree of friction reduction performance, thereby extending service life when compared to conventional water transport RAPPs.
It is further desired that such RAPPs comprising such construction provide the improved degree of friction reduction performance in a manner that avoids the need to filter the incoming water to ultra-fine standards, thereby reducing the overall equipment and labor costs associated with RAPP operation. Finally, it is desired that such RAPP be constructed in a manner avoiding the use of exotic materials and/or nonconventional manufacturing techniques, thereby minimizing any such impact on material and manufacturing costs.